1. Technical Field
The present invention relates to a metallic flat seal, in particular a cylinder head gasket, comprising a sealing bead and an embossed anti-slip protection and/or embossed additional seal.
2. Related Art
The sealing function of metallic flat seals is generated, among other things, by forming sealing beads which effect local compression increases and enclose passageways such as cylinder openings, water and oil passages in a closed manner. At the sealing bead, one or a plurality of linear sealing zones is generated. Sealing beads can be formed as half bead or full bead.
However, sealing beads function optimally only in a limited range of deformation. On the one hand, a minimum compression has to be ensured so as to generate a sealing by a slight and elastic deformation of the sealing bead. On the other, the sealing bead must not be pressed completely flat, in particular must not be plastically deformed but has to remain elastic because otherwise the sealing effect gets lost. Thus, it has to be ensured during engine operation that the sealing bead can function within a range of elastic deformation.
In order to prevent a complete flattening, so-called compression limiters or stoppers are used. This involves local thickness increases next to a sealing bead. The maximum thickness of the compression limiter is selected such that a minimum deformation is possible and, at the same time, the minimum is such that the maximally possible deformation under pressure is not high enough to plastically deform the sealing bead.
In case of cylinder head gaskets for engines having more than one cylinder, compression limiters can be configured in a spectacles-like shape (i.e. in the form of connected rings). Flanging layers for forming a stopper is possible; however, it is less flexible and is possible only at the edge of layers of the seal. Seals with compression limiter and a layer therebelow are known, wherein a coating material is provided between the compression limiter and said layer. For fastening additional stopper layers, it is known to fasten the compression limiters onto functional layers, spacer layers or also protective layers by means of laser welding or mechanical joining techniques.
However, in case of these ways of fastening stoppers as additional layer, there is the risk that the compression limiter or the stopper gland shifts during the operation of the engine. Also, it is possible that leaking gas penetrates or escapes between the stopper layer and the adjacent layer or, in general, between any layers. In the prior art, this is prevented by coatings which are applied onto one of the respective layers.